The present invention relates to a device of the type generally known as a crank connector to be positioned between the lower part of a drill string and a downhole motor rotating a drill bit, such coupling permitting to adjust the orientation of the drill path.
Many methods and devices have been proposed heretofore for carrying out directional drilling.
According to U.S. Pat. No. 3,365,007, the action of a suitably directed fluid jet is used for locally destroying ground formations so as to create a recess where the drill bit will be diverted. Obviously such a device cannot be accurate since the jet action and thus the resulting bit deflection will vary with the hardness of the geological formations. Moreover it is necessary to use a special drill bit provided with a nozzle for discharging the fluid jet.
According to another method, which is for example described in British Pat. No. 1,139,908, U.S. Pat. Nos. 3,593,810, 3,888,319, and 4,040,494 or in French Pat. No. 2,297,989, there is used a deflecting device surrounding a section of the drill string at its lower part, usually in the vicinity of the drill bit. This deflecting device is provided with a plurality of radial fingers displaceable with respect to the drill string axis. By suitably displacing these fingers which bear on the wall of the drilled borehole, it is possible to offset the drill bit axis with respect to the borehole axis, which results in a deflection of the drilling direction.
With such devices drilling is discontinuous as being performed in successive runs or trips between which drilling is stopped to permit the displacement of the deflecting device. This causes considerable time losses increasing the cost of each drilling operation.
In a present drilling technique making use of a downhole motor, it has been proposed to locate between the lower part of the drill string and the so-called drill head (i.e. the assembly of the drill bit and of the downhole motor) a crank connector of selected angle. However everytime the drilling direction is to be changed it is necessary to raise the whole drill string to the ground surface to change the crank connector to another one of appropriate angle, said angle being selected in dependence with the desired deflection.
New so-called hinged crank connectors have been described in French Pat. No. 1 252 703, or mentioned in French Pat. No. 2 175 620. Such connectors usually comprise two tubular parts hinged to each other and which can only take two relative positions. In a first position the two parts of the connector are aligned (the angle of the connector is then equal to zero), while in the second position of the connector the two parts thereof are at a preselected angle to each other. As with the crank connector of the above-described type it is necessary to raise to the surface at least one constituting element of the connector when the desired drilling deflection is not compatible with the angle which the two parts of the connector can form between each other.